Sci 10 – Class Starter
Date: Oct 16th ,12 Assignment: CYU 9.2 Q’s 1-4
Deducing Balanced Equations
Premise #1: Mass can neither be created nor destroyed
Mass before reaction = Mass after reaction
Premise #2: Mass is a measure of the amount of matter
Matter before reaction = Matter after reaction
Premise #3: Matter is made up of elements each of which
having a certain amount of atoms
# of atoms of element A + # of atoms B of element Before =
# of atoms A + # of atoms B After
Balancing Equations
To Balance equations we will be changing the
coefficients to balance the number of atoms on the
reactants (left) and the products (right)
Question: Why can we only change the coefficients and
not the subscripts?
Is the following Equation Balanced?
O2 + H2  H2O
-O-H-
Balancing Equations
How many atoms of each element do we have on the left? On the right?
Building a Balanced Equation
1. Working at your tables you will each build 10
balanced equations at your table
2. Use the numbers as coefficients to balance the
number of atoms on the left and the right
3. When you have finished record the results in the
table
4. Make sure you finish the entire worksheet
Homework:
• Worksheet: Balancing Equations Challenge!
• CYU 9.2 Q’s 5-8
• Worksheet: Balancing Word Equations
Checkpoint next class!